freezer: remove unused @sig_only from freeze_task()
[linux-3.10.git] / kernel / cgroup_freezer.c
1 /*
2  * cgroup_freezer.c -  control group freezer subsystem
3  *
4  * Copyright IBM Corporation, 2007
5  *
6  * Author : Cedric Le Goater <clg@fr.ibm.com>
7  *
8  * This program is free software; you can redistribute it and/or modify it
9  * under the terms of version 2.1 of the GNU Lesser General Public License
10  * as published by the Free Software Foundation.
11  *
12  * This program is distributed in the hope that it would be useful, but
13  * WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
15  */
16
17 #include <linux/export.h>
18 #include <linux/slab.h>
19 #include <linux/cgroup.h>
20 #include <linux/fs.h>
21 #include <linux/uaccess.h>
22 #include <linux/freezer.h>
23 #include <linux/seq_file.h>
24
25 enum freezer_state {
26         CGROUP_THAWED = 0,
27         CGROUP_FREEZING,
28         CGROUP_FROZEN,
29 };
30
31 struct freezer {
32         struct cgroup_subsys_state css;
33         enum freezer_state state;
34         spinlock_t lock; /* protects _writes_ to state */
35 };
36
37 static inline struct freezer *cgroup_freezer(
38                 struct cgroup *cgroup)
39 {
40         return container_of(
41                 cgroup_subsys_state(cgroup, freezer_subsys_id),
42                 struct freezer, css);
43 }
44
45 static inline struct freezer *task_freezer(struct task_struct *task)
46 {
47         return container_of(task_subsys_state(task, freezer_subsys_id),
48                             struct freezer, css);
49 }
50
51 bool cgroup_freezing(struct task_struct *task)
52 {
53         enum freezer_state state;
54         bool ret;
55
56         rcu_read_lock();
57         state = task_freezer(task)->state;
58         ret = state == CGROUP_FREEZING || state == CGROUP_FROZEN;
59         rcu_read_unlock();
60
61         return ret;
62 }
63
64 /*
65  * cgroups_write_string() limits the size of freezer state strings to
66  * CGROUP_LOCAL_BUFFER_SIZE
67  */
68 static const char *freezer_state_strs[] = {
69         "THAWED",
70         "FREEZING",
71         "FROZEN",
72 };
73
74 /*
75  * State diagram
76  * Transitions are caused by userspace writes to the freezer.state file.
77  * The values in parenthesis are state labels. The rest are edge labels.
78  *
79  * (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN)
80  *    ^ ^                    |                     |
81  *    | \_______THAWED_______/                     |
82  *    \__________________________THAWED____________/
83  */
84
85 struct cgroup_subsys freezer_subsys;
86
87 /* Locks taken and their ordering
88  * ------------------------------
89  * cgroup_mutex (AKA cgroup_lock)
90  * freezer->lock
91  * css_set_lock
92  * task->alloc_lock (AKA task_lock)
93  * task->sighand->siglock
94  *
95  * cgroup code forces css_set_lock to be taken before task->alloc_lock
96  *
97  * freezer_create(), freezer_destroy():
98  * cgroup_mutex [ by cgroup core ]
99  *
100  * freezer_can_attach():
101  * cgroup_mutex (held by caller of can_attach)
102  *
103  * freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
104  * freezer->lock
105  *  sighand->siglock (if the cgroup is freezing)
106  *
107  * freezer_read():
108  * cgroup_mutex
109  *  freezer->lock
110  *   write_lock css_set_lock (cgroup iterator start)
111  *    task->alloc_lock
112  *   read_lock css_set_lock (cgroup iterator start)
113  *
114  * freezer_write() (freeze):
115  * cgroup_mutex
116  *  freezer->lock
117  *   write_lock css_set_lock (cgroup iterator start)
118  *    task->alloc_lock
119  *   read_lock css_set_lock (cgroup iterator start)
120  *    sighand->siglock (fake signal delivery inside freeze_task())
121  *
122  * freezer_write() (unfreeze):
123  * cgroup_mutex
124  *  freezer->lock
125  *   write_lock css_set_lock (cgroup iterator start)
126  *    task->alloc_lock
127  *   read_lock css_set_lock (cgroup iterator start)
128  *    task->alloc_lock (inside __thaw_task(), prevents race with refrigerator())
129  *     sighand->siglock
130  */
131 static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss,
132                                                   struct cgroup *cgroup)
133 {
134         struct freezer *freezer;
135
136         freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
137         if (!freezer)
138                 return ERR_PTR(-ENOMEM);
139
140         spin_lock_init(&freezer->lock);
141         freezer->state = CGROUP_THAWED;
142         return &freezer->css;
143 }
144
145 static void freezer_destroy(struct cgroup_subsys *ss,
146                             struct cgroup *cgroup)
147 {
148         struct freezer *freezer = cgroup_freezer(cgroup);
149
150         if (freezer->state != CGROUP_THAWED)
151                 atomic_dec(&system_freezing_cnt);
152         kfree(freezer);
153 }
154
155 /*
156  * The call to cgroup_lock() in the freezer.state write method prevents
157  * a write to that file racing against an attach, and hence the
158  * can_attach() result will remain valid until the attach completes.
159  */
160 static int freezer_can_attach(struct cgroup_subsys *ss,
161                               struct cgroup *new_cgroup,
162                               struct task_struct *task)
163 {
164         struct freezer *freezer;
165
166         /*
167          * Anything frozen can't move or be moved to/from.
168          */
169
170         freezer = cgroup_freezer(new_cgroup);
171         if (freezer->state != CGROUP_THAWED)
172                 return -EBUSY;
173
174         return 0;
175 }
176
177 static int freezer_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
178 {
179         return cgroup_freezing(tsk) ? -EBUSY : 0;
180 }
181
182 static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
183 {
184         struct freezer *freezer;
185
186         /*
187          * No lock is needed, since the task isn't on tasklist yet,
188          * so it can't be moved to another cgroup, which means the
189          * freezer won't be removed and will be valid during this
190          * function call.  Nevertheless, apply RCU read-side critical
191          * section to suppress RCU lockdep false positives.
192          */
193         rcu_read_lock();
194         freezer = task_freezer(task);
195         rcu_read_unlock();
196
197         /*
198          * The root cgroup is non-freezable, so we can skip the
199          * following check.
200          */
201         if (!freezer->css.cgroup->parent)
202                 return;
203
204         spin_lock_irq(&freezer->lock);
205         BUG_ON(freezer->state == CGROUP_FROZEN);
206
207         /* Locking avoids race with FREEZING -> THAWED transitions. */
208         if (freezer->state == CGROUP_FREEZING)
209                 freeze_task(task);
210         spin_unlock_irq(&freezer->lock);
211 }
212
213 /*
214  * caller must hold freezer->lock
215  */
216 static void update_if_frozen(struct cgroup *cgroup,
217                                  struct freezer *freezer)
218 {
219         struct cgroup_iter it;
220         struct task_struct *task;
221         unsigned int nfrozen = 0, ntotal = 0;
222         enum freezer_state old_state = freezer->state;
223
224         cgroup_iter_start(cgroup, &it);
225         while ((task = cgroup_iter_next(cgroup, &it))) {
226                 ntotal++;
227                 if (freezing(task) && frozen(task))
228                         nfrozen++;
229         }
230
231         if (old_state == CGROUP_THAWED) {
232                 BUG_ON(nfrozen > 0);
233         } else if (old_state == CGROUP_FREEZING) {
234                 if (nfrozen == ntotal)
235                         freezer->state = CGROUP_FROZEN;
236         } else { /* old_state == CGROUP_FROZEN */
237                 BUG_ON(nfrozen != ntotal);
238         }
239
240         cgroup_iter_end(cgroup, &it);
241 }
242
243 static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
244                         struct seq_file *m)
245 {
246         struct freezer *freezer;
247         enum freezer_state state;
248
249         if (!cgroup_lock_live_group(cgroup))
250                 return -ENODEV;
251
252         freezer = cgroup_freezer(cgroup);
253         spin_lock_irq(&freezer->lock);
254         state = freezer->state;
255         if (state == CGROUP_FREEZING) {
256                 /* We change from FREEZING to FROZEN lazily if the cgroup was
257                  * only partially frozen when we exitted write. */
258                 update_if_frozen(cgroup, freezer);
259                 state = freezer->state;
260         }
261         spin_unlock_irq(&freezer->lock);
262         cgroup_unlock();
263
264         seq_puts(m, freezer_state_strs[state]);
265         seq_putc(m, '\n');
266         return 0;
267 }
268
269 static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
270 {
271         struct cgroup_iter it;
272         struct task_struct *task;
273         unsigned int num_cant_freeze_now = 0;
274
275         cgroup_iter_start(cgroup, &it);
276         while ((task = cgroup_iter_next(cgroup, &it))) {
277                 if (!freeze_task(task))
278                         continue;
279                 if (frozen(task))
280                         continue;
281                 if (!freezing(task) && !freezer_should_skip(task))
282                         num_cant_freeze_now++;
283         }
284         cgroup_iter_end(cgroup, &it);
285
286         return num_cant_freeze_now ? -EBUSY : 0;
287 }
288
289 static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
290 {
291         struct cgroup_iter it;
292         struct task_struct *task;
293
294         cgroup_iter_start(cgroup, &it);
295         while ((task = cgroup_iter_next(cgroup, &it)))
296                 __thaw_task(task);
297         cgroup_iter_end(cgroup, &it);
298 }
299
300 static int freezer_change_state(struct cgroup *cgroup,
301                                 enum freezer_state goal_state)
302 {
303         struct freezer *freezer;
304         int retval = 0;
305
306         freezer = cgroup_freezer(cgroup);
307
308         spin_lock_irq(&freezer->lock);
309
310         update_if_frozen(cgroup, freezer);
311
312         switch (goal_state) {
313         case CGROUP_THAWED:
314                 if (freezer->state != CGROUP_THAWED)
315                         atomic_dec(&system_freezing_cnt);
316                 freezer->state = CGROUP_THAWED;
317                 unfreeze_cgroup(cgroup, freezer);
318                 break;
319         case CGROUP_FROZEN:
320                 if (freezer->state == CGROUP_THAWED)
321                         atomic_inc(&system_freezing_cnt);
322                 freezer->state = CGROUP_FREEZING;
323                 retval = try_to_freeze_cgroup(cgroup, freezer);
324                 break;
325         default:
326                 BUG();
327         }
328
329         spin_unlock_irq(&freezer->lock);
330
331         return retval;
332 }
333
334 static int freezer_write(struct cgroup *cgroup,
335                          struct cftype *cft,
336                          const char *buffer)
337 {
338         int retval;
339         enum freezer_state goal_state;
340
341         if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0)
342                 goal_state = CGROUP_THAWED;
343         else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0)
344                 goal_state = CGROUP_FROZEN;
345         else
346                 return -EINVAL;
347
348         if (!cgroup_lock_live_group(cgroup))
349                 return -ENODEV;
350         retval = freezer_change_state(cgroup, goal_state);
351         cgroup_unlock();
352         return retval;
353 }
354
355 static struct cftype files[] = {
356         {
357                 .name = "state",
358                 .read_seq_string = freezer_read,
359                 .write_string = freezer_write,
360         },
361 };
362
363 static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup)
364 {
365         if (!cgroup->parent)
366                 return 0;
367         return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files));
368 }
369
370 struct cgroup_subsys freezer_subsys = {
371         .name           = "freezer",
372         .create         = freezer_create,
373         .destroy        = freezer_destroy,
374         .populate       = freezer_populate,
375         .subsys_id      = freezer_subsys_id,
376         .can_attach     = freezer_can_attach,
377         .can_attach_task = freezer_can_attach_task,
378         .pre_attach     = NULL,
379         .attach_task    = NULL,
380         .attach         = NULL,
381         .fork           = freezer_fork,
382         .exit           = NULL,
383 };